Transcription is the major control point of gene expression and RNA polymerase (RNAP) is the central enzyme of transcription. Our long-term goal is to understand the mechanism of transcription and its regulation. Determining the threedimensional structures of RNAP is an essential step. This is best accomplished with highly characterized prokaryotic RNAPs, especially because of the high degree of structural and functional homology with RNAPs from bacteria to man. Our main aim is to solve the structure of the RNAP to as high a resolution as possible. The aim of this specific experiment is to collect native data to as high a resolution as possible, and to collect more data on potential heavy-metal derivatives (with anomalous data, if possible). Our main experimental objective would be to obtain a native data set to higher resolution than what we currently have obtained (3.2 A). Additionally, we are currently working to prepare and crystallize RNAP completely substituted with Se-methionine. If available, we would collect this data as well. Additionally, we would like to collect more data on potential heavy-metal derivatives. Data collection was done on BioCARS Station 14 BM-C.